This severe storm in northeast Colorado was producing a gust front and rotating at the same time. Note the cyclonic banding above the outflow on the left side of the image (west) where the storm is approaching. An old cell to the east is providing and outflow boundary for the storm to ride along. It never produced a tornado, but storms that have both these features of rotation, and strong straight line winds can cause considerable property damage.
Atmospheric conditions did support a tonado out of another storm about 40 mile south of this cell an hour later. The image was taken near Akron, Colorado.
Gust Front Appearance in a Rotating Supercell
The storm pictured here on first glance would appear to be a gust front storm but looks are deciving. Not the small tree on the east side of the small town (or just left of center). It's leaning over to the west as strong winds feed into the storm. The shelf appearance does not guarantee the storm is a gust front producer or in an outflow stage. In this particular case the storm produced a confirmed tornado with F-2 damage about an hour and a half after this picture was taken. After dark, I watch with a group of chasers as an elephant trunk tornado formed about a mile west of our position, but we were unable to capture it in the lightning.
Severe Colorado Hail and Wind Storm that is not Rotating
A Colorado storm is pictured here that moved northeast into far southwestern Nebraska. It looks somewhat similar to the previous storm, but is not rotating and blasted us with strong straight winds and hail. If you see a storm like this watch the motion on the top of the shelf cloud. Is it pushing out, or rotating back into the storm? This one was pushing out. Also, watch in wind direction under the leading edge to see if the storm has inflow like the two pictured above or winds are gusting our and away from the storm.
Squall Line with a Stacked Shelf Cloud
Vehicles rush to beat the storms approaching from the north. This is an example of a typical squall line with strong straight line winds, heavy rain and hail. The leading edge of the clouds brings a cold wind shift coming out of the storm. The cold air works like a shovel scooping up moisture and forming new convection and storms on the leading edge of the outflow.
Severe Colorado Hail and Wind Storm
This storm produced high winds on the leading edge of the gust front and then battered homes with large hail. The clouds on this outflow boundary were horizontally turning over as it rushed out to the east. The temperature dropped dramatically, which is usually the case during summer thunderstorms on the high plains.
Strong Straight Line Winds and a Dangerous Gustnado
This storm produced straight line wind over 80 m.p.h. and caused considerable property damage in rural sections of north central Oklahoma. This was part of a line of storms producing widespread high wind over a large of northern Oklahoma. The cloud base was quite high, about 7,000 feet above ground level, and the large cloud of dust is over 3,000 feet high and a quarter mile wide at the bottom. It was rotating violently, and produced an audible roar that could be heard for about 2 miles. This (straight line) wind driven "spin up" lasted for over 10 minutes while I drove toward it and another 5 minutes after I got in front of it. It was in the earlier days of my chasing and I had no idea how powerful such a vortex could be. The circulation propagated along at the speed of the outflow, but was rotating faster than the surrounding winds. When I heard the loud roar and saw trees and shrubs flying apart I made a hasty retreat. Circulations such as this must be rare and this is the only one I have witnessed. As a tornado, I estimate it would be only rated at F-1 which is weak, but certainly a storm that demands respect. More commonly gustnadoes are smaller and short lived. On days when conditions are correct multiple gustnados may occur. These gustnados did have a circulation at cloud base.
Monster Gust Front
A cranked up gust front roaring across the countryside. This is known as an arcus-gust front. Note the arc shape to the outflow and the dust being carried into the air. These storm can move at 60 plus m.p.h. and usually deliver more dirt that rain since the precipitation area is narrow and it moves by fast. Tornadoes get the headlines, but these storms can create wide spread damage.
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